Hydrocarbon fluids find widespread use as solvents such as in adhesives, cleaning fluids, explosives solvents for decorative coatings and printing inks, light oils for use in applications such as metalworking or demoulding and industrial lubricants, and drilling fluids. The hydrocarbon fluids can also be used as extender oils in adhesives and sealant systems such as silicone sealants and as viscosity depressants in plasticised polyvinyl chloride formulations and as carrier in polymer formulation used as flocculants for example in water treatment, mining operations or paper manufacturing and also used as thickener for printing pastes. Hydrocarbon fluids may also be used as solvents in a wide variety of other applications such as chemical reactions.
The chemical nature and composition of hydrocarbon fluids varies considerably according to the use to which the fluid is to be put. Important properties of hydrocarbon fluids are the distillation range generally determined by ASTM D-86 or the ASTM D-1160 vacuum distillation technique used for heavier materials, flash point, density, Aniline Point as determined by ASTM D-611, aromatic content, sulphur content, viscosity, colour and refractive index. Fluids can be classified as paraffinic, isoparaffinic, dearomatised, naphthenic, non-dearomatised and aromatic.
These fluids tend to have narrow boiling point ranges as indicated by a narrow range between Initial Boiling Point (IBP) and Final Boiling Point (FBP) according to ASTM D-86. The Initial Boiling Point and the Final Boiling Point will be chosen according to the use to which the fluid is to be put. However, the use of the narrow cuts provides the benefit of a precise flash point which is important for safety reasons. The narrow cut also brings important fluid properties such as a better defined aniline point or solvency power then viscosity, and defined evaporation conditions for systems where drying is important, and finally better defined surface tension.
U.S. Pat. No. 4,036,734 discloses a process for converting aromatics into naphthenics. The process comprises two hydrogenation stages. The first hydrogenation stage is operated at a temperature from 204 to 315° C., a pressure from 6.9 to 103.5 bar, a liquid hourly space velocity of 0.5 to 10 hr−1, and hydrogen treat rate of 0.034 to 0.34 Nm3/liter of feed. The flow exiting the first stage comprises H2S which is disposed of and a solvent which is further hydrogenated in a second stage. The first stage operates under hydrodesulphurisation conditions. The second stage is operated at a temperature from 149 to 315° C., a pressure from 17.3 to 138 bar, a liquid hourly space velocity of 0.2 to 5 hr−1, and a hydrogen treat rate of 0.08 to 0.51 Nm3/liter of feed The final resulting fluid is said to have a boiling range which can be from 272° C. to 401° C., and aromatics contents up to 4.3% by weight, the lowest value reported being 0.4% by weight. The lowest value is obtained for the solvent having the lowest boiling range.
WO-A-03/074634 and WO-A-03/074635 are both directed to the production of fluids comprising at least 40% naphthenics and a narrow boiling range. In these two documents, the initial feed is a Vacuum Gas Oil (VGO), that is then subjected to hydrocracking. A typical VGO is disclosed as having the following properties:
Specific Gravity: 0.86-0.94;
ASTM D-1160 distillation: IBP 240-370° C., FBP 380-610° C. (here ASTM D-1160 is used due to the high Final Boiling Point);
Aromatics wt %: 1 ring from 13 to 27%, 2 rings from 10 to 20%, 3 rings from 7 to 11%, 4 rings from 6 to 12%, total from 40 to 65;
Naphthenes wt %: ring from 2 to 4%, 2 rings from 4 to 7%, 3 rings from 4 to 6%, 4 rings from 4 to 7%, total from 16 to 27;
Paraffins wt %: from 7 to 16%;
IsoParaffins wt %: from 8 to 20%;
Sulphur: from 1.75 to 3 wt % (as measured by ASTM D-2622 using X-Ray Fluorescence);
This VGO is then hydrocracked into a feedstock.
The feedstocks have low sulphur content, typically 1 to 15 ppm by weight. These feedstocks have also a low aromatic content, typically 3 to 30 wt % (this is said to be lower than the typical range of 15 to 40 wt % in conventional fluid manufacture).
It is indicated that the lower sulphur content can avoid or reduce the need for deep hydrodesulphurisation and also results in less deactivation of the hydrogenation catalyst when hydrogenation is used to produce dearomatised grades. The lower aromatic content also diminishes the hydrogenation severity required when producing dearomatised grades thus allowing the debottlenecking of existing hydrogenation units or allowing lower reactor volumes for new units.
It is further indicated that the resulting products have a high naphthenics content, typically at least 40%, preferably at least 60%.
Hydrogenation of the hydrocracked VGO is said to be operated at a temperature of 200° C., a pressure of 27 bar, a liquid hourly space velocity of 1 hr−1, and a treat rate of 200 Nm3/liter of feed.
While these two documents indicate that the final product has a very low content in aromatics, the fact is that high boiling products still contain a high amount of aromatics. The product having a boiling range of 237° C. to 287° C. is said to contain 42 ppm of aromatics. The three other products having higher boiling ranges (308° C.-342° C., 305° C.-364° C. and 312° C.-366° C.) have aromatics contents of about 2000 ppm.
Thus, the production of fluids having high boiling ranges, typically with an Initial Boiling Point above 300° C., together with very low aromatics content, typically below 100 ppm, is still not taught in the prior art.
EP1447437 discloses a process in which a first stream of hydrocarbons having an aromatics content of at least 70% is subjected to hydrodesulphurization so as to obtain a first stream with a sulphur content of less than 50 ppm, and step of hydrogenation. In this process, the first stream is said to have a distillation interval of 145-260° C., and the example provides for 142-234° C. It is also indicated that the hydrogenated stream can be fractionated, e.g. in light cuts of 100-205° C., middle cuts of 170-270° C. and heavy cuts of 200-400° C. Yet, in the sole example, there is no fractionation taking place. It is suggested in this EP1447437 the desulphuration and hydrogenation of a Light cycle oil fraction from the effluents of an FCC unit. It is however shown that even if the naphthenic content is high (86.5 wt %) which suggests good solvency, the aromatic content remains at 100 ppm.
WO01/083640 discloses that some specific cuts are gas oil cuts resulting from hydrocracking petroleum loads with the gas oil cuts undergoing a forced hydrogenation stage to eliminate aromatic compounds followed by fractionation.
The invention thus aims at providing a process for making products having a very low content in aromatics, typically below 100 ppm, and this even for products having an Initial Boiling Point above 300° C., especially for aliphatic (paraffinic and naphthenic) fluids.